The present invention relates to a two-stage process for obtaining a substantial amount of olefinic product from a residua feedstock. The first stage is comprised of a thermal process unit containing a reaction zone comprised of a horizontal moving bed of fluidized hot particles operated at temperatures from about 500.degree. to 600.degree. C. and having a short vapor residence time, and the second stage thermal conversion zone operated at a temperature of about 700.degree. C. to about 1100.degree. C., and also having a short vapor residence time, preferably shorter than that of the first stage reaction zone.